Extended life fluorescence polyvinyl chloride sheeting

ABSTRACT

An extended life fluorescent polyvinyl chloride sheeting and a method for forming the sheeting are disclosed. The sheeting includes a polyvinyl chloride film having a fluorescent colorant incorporated therein. A protective polymer layer is attached to the polyvinyl chloride film. A light filtering agent is incorporated into the protective layer, wherein the filter agent blocks the 425 nm and lower wavelengths of the visible spectrum.

RELATED APPLICATION

This present application claims the benefit of U.S. Provisional PatentApplication No. 60/072,026, filed on Jan. 21, 1998. This application isa continuation of application Ser. No. 09/233,965, filed on Jan. 20,1999 now U.S. Pat. No. 6,191,200. The entire teachings of eachapplication are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The advantages of the high visibility of fluorescent materials is wellknown. However, poor color fastness in the presence of sunlight has madetheir use in some applications limited to short-lived, temporaryapplications. These applications include roadside work zone signs,vehicle conspicuity signs, etc.

Plasticized polyvinyl chloride has been used extensively forretroreflective sheeting applications. In roadside work zoneapplications, flexible, roll-up signage formed of polyvinyl chlorideprovides an improved safety upon impact by a vehicle over rigid signage.However, the fluorescent colored polyvinyl chloride signs can fade to aclear film quickly after exposure to sunlight as the fluorescentcolorant is consumed with lengthy exposure to ultraviolet light emittedby the sun. However, the retroreflective prism structure continues tofunction.

Some polymers, such as polycarbonate, that have a fluorescent colorantinclude a hindered amine light stabilizer compound.

SUMMARY OF THE INVENTION

The present invention includes an extended life fluorescent polyvinylchloride sheeting and a method for forming the sheeting.

The sheeting includes a polyvinyl chloride film having a fluorescentcolorant incorporated therein. A protective polymer layer is attached tothe polyvinyl chloride film. A light filtering agent is incorporatedinto the protective polymer layer, wherein the filter agent blocks the425 nm and lower wavelengths of the visible spectrum.

The method includes providing a polyvinyl chloride film having afluorescent colorant incorporated therein. A protective polymer layer isattached to the polyvinyl chloride film. The protective polymer layerincludes a light filtering agent that blocks the 425 nm and lowerwavelengths of the visible spectrum, thereby forming the extended lifefluorescent polyvinyl chloride sheeting.

The present invention has an advantage of providing fluorescentprotection to a polyvinyl chloride sheeting while providing solventresistance, printability, low coefficient of friction and canincorporate water shedding properties, such as hydrophobic andhydrophilic additives where desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart of the results of an accelerated weathering color testof a first sample of the present invention and a first standard product.

FIG. 2 is a chart of the results of an accelerated weathering color testof a second sample of the present invention and a second standardproduct.

FIG. 3 is a chart of the results of an accelerated weathering color testof the second sample of the present invention and second and thirdstandard products.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention. All percentagesand parts are by weight unless otherwise indicated.

Retroreflective materials are typically formed of a sheet ofthermoplastic, which has a colorant mixed therein with the polymers.Attached to the sheet of thermoplastic is an array of cube-corner orprismatic retroreflectors as described in U.S. Pat. No. 3,712,706,issued to Stamm on Jan. 23, 1973, the teachings of which areincorporated herein in their entirety by reference. Generally, theprisms are made by forming a master die on a flat surface of a metalplate or other suitable material. To form the cube-corner, three seriesof parallel equidistant intersecting V-shaped grooves 60 degrees apartare inscribed in the plate. The die is then used to process the desiredcube-corner array into a flat plastic surface. When the groove angle is70 degrees, 31 minutes, 43.6 seconds, the angle formed by theintersection of two cube faces (dihedral angle) is 90 degrees and theincident light is retroreflected back to the source.

The efficiency of a retroreflective structure is the measure of theamount of incident light returned within a cone diverging from the axisof retroreflection. A distortion of the prismatic structure adverselyaffects the efficiency. Furthermore, cube-corner retroreflectiveelements have low angularity at some orientation angles, for instance,the elements will only brightly reflect light that impinges on it withina narrow angular range centering approximately on its optical axis. Lowangularity arises from the inherent nature of these elements which aretrihedral structures having three mutually perpendicular lateral faces.The elements are arranged so that the light to be retroreflectedimpinges into the internal space defined by the faces, and theretroreflection of the impinging light occurs by internalretroreflection of the light from face to face of the element. Impinginglight that is inclined substantially away from the optical axis of theelement (which is a trisection of the internal space defined by thefaces of the element) strikes the face at an angle less than itscritical angle, thereby passing through the face rather than beingreflected. Further details concerning the structures and the operationof cube-corner microprisms can be found in U.S. Pat. No. 3,684,348,issued to Rowland on Aug. 15, 1972, the teachings of which areincorporated by reference herein in their entirety. The disclosed methodis for forming cube-corner microprisms in a cooperatively configuredmold. The prisms are bonded to sheeting which is applied thereover toprovide a composite structure in which cube-corner microprisms projectfrom one surface of the sheeting.

The array of retroreflectors includes optical elements that are known inthe art, such as cube-corner prisms, four-sided prisms, Fresnel lenses,rounded lenses, etc. In one embodiment, the array of retroreflectors hasa window side and a facet side. The array of retroreflectors are formedof a transparent flexible polymer polyvinyl chloride. Preferably, thepolymer is cast in a mold with a monomer or oligomer, and thepolymerization is initiated by ultraviolet radiation. Preferably, thearray of retroreflectors is formed of cube-corner prism elements havinga length along each cube side edge in the range of between about 0.003and 0.02 inches (0.076 and 0.51 mm). In a preferred embodiment, theprism elements have a length along each cube-side edge in the range ofbetween 0.0049 and 0.02 inches (0.124 and 0.51 mm). In a particularlypreferred embodiment, each cube-side edge has a length of about 0.0049inches (0.124 mm).

An adhesive can be applied to the prism facets for attaching a backinglayer to the retroreflective structure. If an adhesive is employed onthe prism facets, the adhesive can cause the surface of the prisms towet, thereby destroying the air interface and eliminating the ability ofthe prism to retroreflect. As a result, the reflective coating ispreferably deposited on the surface of the dihedral facets. Typically,the reflective coating is formed by sputtering aluminum, silver or goldor by vacuum metalization. Alternatively, metal lacquers, dielectriccoatings and other specular coating materials can be employed.

The retroreflective structure 24 can be formed by numerous methods. Someof the methods for forming a retroreflective structure are disclosed inU.S. Pat. No. 3,684,348, issued to Rowland on Aug. 15, 1972; U.S. Pat.No. 3,689,346, issued to Rowland on Sep. 5, 1972; U.S. Pat. No.3,811,983, issued to Rowland on May 21, 1974; U.S. Pat. No. 3,830,682,issued to Rowland on Aug. 20, 1974; U.S. Pat. No. 3,975,083, issued toRowland on Aug. 17, 1976; U.S. Pat. No. 4,332,847, issued to Rowland onJun. 1, 1982; U.S. Pat. No. 4,801,193, issued to Martin on Jan. 31,1989; U.S. Pat. No. 5,229,882, issued to Rowland on Jul. 20, 1993; U.S.Pat. No. 5,236,751, issued to Martin et al. on Aug. 17, 1993; U.S. Pat.No. 5,264,063, issued to Martin on Nov. 23, 1992; U.S. Pat. No.5,376,431, issued to Rowland on Dec. 27, 1994; U.S. Pat. No. 5,491,586,issued to Phillips on Feb. 13, 1996; U.S. Pat. No. 5,512,219, issued toRowland on Apr. 30, 1996; U.S. Pat. No. 5,558,740, issued to Bernard etal. on Sep. 24, 1996; U.S. Pat. No. 5,592,330, issued to Bernard on Jan.7, 1997; and U.S. Pat. No. 5,637,173, issued to Martin et al. on Jun.10, 1997. The teachings of each patent are incorporated herein byreference.

The advantages of the high visibility of fluorescent materials is wellknown, but their poor color fastness in the presence of ultravioletlight has made their use in some important applications, such asroadside work zone, vehicle conspicuity, etc., limited to short-lived,temporary applications.

Plasticized vinyl has been used extensively for retroreflective sheetingapplications. In applications, such as roadside work zones, it has alsobeen well established that flexible so-called “roll-up” signage usuallymade of highly plasticized polyvinyl chloride provide greatly improvedsafety upon impact over rigid signage.

The use of a free radical absorber of the hindered amine lightstabilizer type, such as 2,2,6,6-tetramethyl piperdine, has been used toimprove the color fastness of polycarbonate colored with thethioxanthene, perylene imide, and thioindigold fluorescent colorants(U.S. Pat. No. 5,605,761).

It has been found that by use of a protective polymer layer or coatingor film layer made of polyacrylate, polyurethane, or polyurethaneacrylates which incorporate ultraviolet absorbers of the benzophenone orbenzotriazole-type along with a light filtering agent which blocks outthe short wavelengths of the visible spectrum (425 nm and lower) over ahighly plasticized flexible fluorescent polyvinyl chloride sheetingcontaining a suitable hindered amine, color fastness can be greatlyimproved. The wavelengths of visible light extend between about 400 nmfor the extreme violet and about 720 nm for the deep red. The visiblelight filtering agent should impart color that can obscure the desirabledaytime visibility of the fluorescent product. A suitable visible lightfiltering agent is Color Index Solvent Yellow 93. A suitable amount offiltering agent is in a range of between about 0.05 and 5.0 percent. Apreferred range is between about 1.0 and 1.5 percent. A suitablehindered amine for use with polyvinyl chloride isbis-(1,2,2,6,6-tetramethyl-4-piperidinyl) sebacate. A suitable amount ofhindered amine is in a range of between about 0.1 and 7.0 percent. Apreferred range is between about 0.2 and 1.5 percent.

Through selection of coating ingredients in the top coat protectivepolymer layer, the fluorescent protection features can be coupled with awide variety of different performance properties including but notlimited to cold temperature flexibility, solvent resistance,printability, low coefficient of friction, and specialized watershedding properties (i.e. hydrophobic, hydrophilic).

The colors of principal interest in the area of fluorescentretroreflective sheeting are lime-yellow and red-orange.

The base material of wavelength filtering layer can be a polymer film,such as polyvinyl chloride, polyacrylate, polyurethane, polyvinylidenechloride, fluoropolymer, or highly stabilized copolymers, such asvinylidene fluoride-hexafluoropropylene. This film can be laminateddirectly to fluorescent colored layer through heat and pressure in somecases, such as some urethanes, or by use of an adhesive layer. Thethickness of the wavelength filtering layer can be in the range ofbetween about 0.1 and 10 mils (0.00254 and 0.254 mm). The base materialof the wavelength filtering layer can also be applied to the fluorescentcolored layer as a coating. This coating can be solvent borne,water-based, two-part, or radiation curable in nature.

The wavelength filtering layer is protective to the colorant in thefluorescent colored layer by incorporation of ultraviolet lightabsorbers or selected colorants or both which can block the wavelengthsthat are destructive to the colorant but still allow the day brightcolor to be visible. The daytime visibility of the product can betemporarily enhanced by the incorporation of some fluorescent colorantinto the wavelength filtering layer, provided that the wavelengthsgenerated by fluorescent colorant in the filtering layer are notdestructive to the primary fluorescent colorant in the fluorescentcolored layer.

For the fluorescent colored layer, a base polymer of polyvinyl chlorideis preferred. Incorporated into this layer is the primary fluorescentcolorant of the product. The most commonly used, widely available, andlowest cost fluorescent colorants are the xanthene based fluorescentdyes. This group, which encompasses both the fluorenes and thefluorones, includes such dyes as fluoresceins, rhodamines, eosines,phloxines, uranines, succineins, sacchareins, rosamines, and rhodols.The dyes are noted for their brilliant daytime colors, high intensitycolor compatible fluorescence, and poor light fastness. Otherfluorescent dyes displaying better light fastness include pyranines,anthraquinones, benzopyrans, thioxanthenes and perylene imides.

The prism layer can be compression molded or cast directly onto thefluorescent colored layer or attached by means of a tiecoat. The prismlayer can be formed of polyvinyl chloride, an acrylate or other suitablepolymer.

This prismatic sheeting configuration can be sealed to any number ofbacking materials by radio frequency, thermal, or sonic welding methods.The daytime color saturation (chroma) properties of a transparentfluorescent material are increased if backed by a white layer, it isdesirable to have the backing be white in color on the surface behindthe prisms. Alternatively, the prismatic material can be metalized in anaesthetically appealing pattern and laminated to a white pressuresensitive substrate adhesive. Similarly, a pattern can be printed ontothe film prior to casting, or onto the backs of the prisms aftercasting, using a white ink to enhance the daytime chroma. However, thesemethods enhance the daytime fluorescent color at the expense of some ofthe retroreflective area, because the non-metalized prisms that havetheir facets covered with adhesive do not maintain a differentiation inrefractive index that is sufficiently large for internal reflection tooccur.

Both of the latter construction alternatives have the advantage of nothaving an air gap in the construction behind the prism layer.Elimination of the air gap can help augment the physical durability ofthe sheeting, because each layer of the product has about 100% of itssurface bonded to its adjacent layers.

If a reflective material that is environmentally stable yet whiter thanaluminum can be coated onto the prism facets, it can allow a fullymetalized product to have an adequate “cap Y” to produce a desireddaytime color. Silver, chromium, gold, palladium, and platinum are alsopossibilities.

The product can conform to the Minnesota Department of TransportationSpecification 1710 for Fluorescent Orange Retroreflective Sheeting forUse on Work Zone Traffic Control Devices, the teachings of which areincorporated herein by reference in their entirety. It defines a colorbox (see Product Testing Requirements and Specification section),reflectance limits (30 minimum new, 20 minimum to 45 maximum forweathered (500 Weatherometer hours)), and a table (B) of MinimumCoefficients of Retroreflection approximate the 1,300 hour colorretention in a xenon lamp accelerated weathering device.

A series of test samples was prepared for accelerated weathering testingunder ASTM G26. The teachings of ASTM G26 are incorporated herein byreference in their entirety.

EXAMPLE 1

A fluorescent lime (yellow-green) colored microprismatic product wasformed having a polyvinyl chloride base film. The polyvinyl chloridebase film was highly plasticized using phthalate monomeric plasticizersand a xanthene solvent yellow as a colorant with a benzophenoneultraviolet absorber additive having a thickness of about 250μ thick.The film was further protected with a 7μ thick topcoat based on aflexible urethane acrylate oligomer, and containing a benzotriazoleultraviolet absorber and a hindered amine light stabilizer, and C.I.Solvent Yellow 93. This configuration of polyvinyl chloride andadditives absorbed eighty-five percent or more of the light havingwavelengths of 450 nm and shorter.

EXAMPLE 2

A fluorescent orange colored microprismatic product was formed having apolyvinyl chloride base film. The 350μ thick polyvinyl chloride basefilm was highly plasticized using phthalate monomeric plasticizers andcolored with a fluorescent orange, thioxanthone colorant, a benzophenoneultraviolet absorber additive, and hindered amine light stabilizer. Thefilm was further protected with a clear, 100μ thick, polyvinyl chloridebased top film containing a benzophenone ultraviolet absorber additive.

EXAMPLE 3

A fluorescent orange colored microprismatic standard Product A wasformed having a polyvinyl chloride base film. The 250μ thick, polyvinylchloride base film was highly plasticized using phthalate monomericplasticizers and a mixture of a xanthene solvent yellow and rhodamine Bas colorants.

EXAMPLE 4

A fluorescent orange colored microprismatic standard Product B wasformed having a polyvinyl chloride base film. The polyvinyl chloridebase film is highly plasticized using phthalate monomeric plasticizers.The film was made from a lamination of two 150μ thick polyvinyl chloridefilms. The first polyvinyl chloride film included a non-fluorescent butvery light stable combination of a transparent diazo yellow and organicred pigments. The second polyvinyl chloride film included the highlyfluorescent but comparatively fugitive combination of colorants used inStandard Product A.

EXAMPLE 5

A fluorescent lime (yellow-green) colored microprismatic standardProduct C was formed having a polyvinyl chloride base film. The 250μthick, polyvinyl chloride base film was highly plasticized usingphthalate monomeric plasticizers and a xanthene solvent yellow colorant.

All of the aforementioned Examples 1-5 included the same microprismaticarray composed of a cross-linked acrylated urethane ester. Each of theprismatic films was sealed by radio frequency welding to a polymericplasticized, opaque white, textured, polyvinyl chloride backing materialfor purposes of this accelerated weather testing.

All of the samples were mounted onto an aluminum panel with pressuresensitive adhesive and tested in an Atlas model C35 Xenon Weatherometerin accordance with the ASTM G26 test method for a total of 1,500 hours.The teachings of ASTM G26 are incorporated herein in their entirety. Thesamples were evaluated periodically throughout the duration of the testfor color change using a HunterLab LabScan II, LS-6000Spectrophotometer.

Minimal movement in color coordinates can show color stability. Theorange colorant in a standard product can fade to yellow (out of thecolor box) after approximately 48 hours in a carbon-arc Weatherometerwhile the orange colorant in a sample of the present invention can stillbe in the color box after fifteen hundred hours of exposure. An exampleof a color box is shown in FIG. 2 as defined by the orange color regionboundary (Coordinate 1, x=0.550, y=0.360; Coordinate 2, x=0.630,y=0.370; Coordinate 3, x=0.581, y=0.418; Coordinate 4, x=0.516,y=0.394). The color box coordinates are disclosed in ASTM D4956-95,Table 10 for Color Specification Limits (Daytime) for white, yellow,orange, green, red, blue and brown. The teachings of ASTM D4965-95 areherein incorporated by reference in their entirety. Spectrophotometer orcolorimeter having 45°/0° or 0°/45° illumination and viewing geometry issuitable for measuring color. Color coordinates are defined bytristimulus coordinates corresponding to the CIE 1931 StandardColorimetric System by standard illuminant C.

FIG. 1 shows the degree of color change (distance moved) in CIE 1931standard color space for Standard Product C (described in Example 5)after 375 hours of testing was greater than the sample described inExample 1 after 1,500 hours of exposure testing. The date point labelsindicate hours of exposure in the Weatherometer.

FIG. 2 shows the rapid color change of fluorescent orange StandardProduct A (as described in Example 3) after only 100 hours of exposurewhich resulted in a change in color from orange (0.595, 0.4) to yellow(0.498, 0.47) as compared to the color stability of a sample of thepresent invention, as described in Example 2, after 1,500 hours ofexposure, which maintained its orange color.

FIG. 3 shows the color fastness performance of two commerciallyavailable products compared to the present invention as described inExample 2. Standard Product B (Example 4) exhibited rapid color changeover the first 125 hours of exposure as the conventional fluorescentcolorants faded and then became fairly stable between 125 hours and1,500 hours when the non-fluorescent pigments are responsible for thecolor. The Standard Product C (Example 5) also demonstrated a greaterover all color change than the embodiment of Example 2. A moresignificant fact is that the Standard Product C color loss directionindicates a more significant decrease in chroma (shift to the left).This loss of color saturation in the Standard Product C (Example 5)indicates that the embodiment of Example 2 can have better visibility inreal world daytime applications.

Equivalents

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims. Those skilled in the artwill recognize or be able to ascertain using no more than routineexperimentation, many equivalents to the specific embodiments of theinvention described specifically herein. Such equivalents are intendedto be encompassed in the scope of the claims.

What is claimed is:
 1. An extended life fluorescent polyvinyl chloridesheeting, comprising: a) a polyvinyl chloride film having a fluorescentcolorant and hindered amine light stabilizer incorporated therein; andb) a protective polymer layer, which is attached to said polyvinylchloride film, wherein said protective layer includes an ultravioletabsorber.
 2. The sheeting of claim 1 wherein said fluorescent colorantincludes a xanthene-based fluorescent dye.
 3. The sheeting of claim 2wherein the xanthene-based fluorescent dye includes a dye selected froma group consisting of fluoresceins, rhodamines, eosines, phloxines,uranines, succineins, sacchareins, rosamines, and rhodols.
 4. Thesheeting of claim 1 fluorescent colorant includes a dye selected fromthe group consisting of pyranines, anthraquinones, benzopyrans,thioxanthenes and perylene imides.
 5. The sheeting of claim 1 whereinthe fluorescent colorant includes a dye selected from a group consistingof fluoresceins, rhodamines, eosines, phloxines, uranines, succineins,sacchareins, rosamines, rhodols, pyranines, anthraquinones, benzopyrans,thioxanthenes and perylene imides.
 6. The sheeting of claim 5 whereinsaid protective layer includes a light filtering agent, which isincorporated into said protective layer, said filtering agent blocks the425 nm and lower wavelengths of the visible spectrum.
 7. The sheeting ofclaim 5 wherein said hindered amine includesbis-(1,2,2,6,6-tetramethyl-4-piperidinyl) sebacate.
 8. The sheeting ofclaim 6 wherein said light filtering agent includes Color Index SolventYellow
 93. 9. The sheeting of claim 1 wherein said protective polymerlayer includes a polymer selected from the group consisting ofpolyacrylate, polyurethane, polyurethane acrylate, polyvinyl chloride,polyvinyl acetate and polyvinylidene chloride.
 10. The sheeting of claim5 wherein said ultraviolet absorber is selected from the groupconsisting of benzophenone and benzotriazole.
 11. The sheeting of claim5 wherein said protective polymer layer has a thickness in the range ofbetween about 0.2 mils and about 15 mils.
 12. The sheeting of claim 5wherein said protective polymer layer has a thickness in the range ofbetween about 0.5 mils and about 1.0 mil.
 13. The sheeting of claim 5wherein said polyvinyl chloride film includes a printed pattern.
 14. Thesheeting of claim 13 wherein said polyvinyl chloride film includes aprinted pattern formed of a white ink to enhance daytime chroma.
 15. Thesheeting of claim 5 wherein the polyvinyl chloride film includes ametalized layer thereon.
 16. The sheeting of claim 15 wherein themetalized layer is formed of a metal selected from the group consistingof aluminum, chromium, gold, palladium, platinum and silver.
 17. Aretroreflective structure formed with the fluorescent polyvinyl chloridesheeting of claim
 1. 18. A method for forming an extended lifefluorescent polyvinyl chloride sheeting, comprising: a) providing apolyvinyl chloride film having a fluorescent colorant incorporatedtherein; and b) attaching a protective polymer layer to said polyvinylchloride film, wherein said protective polymer layer includes anultraviolet absorber.
 19. The sheeting of claim 18 wherein thefluorescent colorant includes a dye selected from a group consisting offluoresceins, rhodamines, eosines, phloxines, uranines, succineins,sacchareins, rosamines, rhodols, pyranines, anthraquinones, benzopyrans,thioxanthenes and perylene imides.
 20. The method of claim 19 whereinsaid protective polymer layer includes a light filtering agent thatblocks the 425 nm and lower wavelengths of the visible spectrum, therebyforming the extended life fluorescent polyvinyl chloride sheeting. 21.An extended life fluorescent sheeting, comprising: a) a polyvinylchloride film having a fluorescent colorant and hindered amine lightstabilizer incorporated therein; b) a protective polymer layer, which isattached to said polyvinyl chloride film, wherein said protective layerincludes an ultraviolet absorber and wherein said protective polymerlayer includes a polymer selected from the group consisting ofpolyacrylate, polyurethane, polyurethane acrylate, polyvinyl acetate andpolyvinylidene chloride.
 22. The sheeting of claim 21 wherein thefluorescent colorant includes a dye selected from a group consisting offluoresceins, rhodamines, eosines, phloxines, uranines, succineins,sacchareins, rosamines, rhodols, pyranines, anthraquinones, benzopyrans,thioxanthenes and perylene imides.
 23. The extended life fluorescentsheeting of claim 22 wherein said protective layer includes a lightfiltering agent, which is incorporated into said protective layer, saidfiltering agent blocks the 425 nm and lower wavelengths of the visiblespectrum.
 24. The sheeting of claim 22 wherein said ultraviolet absorberis selected from the group consisting of benzophenone and benzotriazole.25. The sheeting of claim 22 wherein said hindered amine includesbis-(1,2,2,6,6-tetramethyl-4-piperidinyl)sebacate.
 26. The sheeting ofclaim 22 wherein said light filtering agent includes Color Index SolventYellow 93.